WAEC Chemistry questions: Chemical combination

27 questions with answers and explanations. Tap an option to check yourself.

1. Question 21· Chemical combination· WAEC

   What mass of calcium oxide is formed by heating 50 g of calcium trioxocarbonate(IV) to constant mass? [Ca = 40, C = 12, O = 16]

   • A50 g
   • B56 g
   • C22 g
   • D28 g

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2. Question 22· Chemical combination· WAEC

   What is the relative molecular mass of CO₂? (C = 12, O = 16)

   • A28
   • B60
   • C32
   • D44

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3. Question 23· Chemical combination· WAEC

   Elements combine in a fixed ratio by mass to form a particular compound. This is the law of

   • Aconservation of mass
   • Bmultiple proportions
   • Cdefinite proportions
   • Dreciprocal proportions

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4. Question 24· Chemical combination· WAEC

   The number of moles in 4.4 g of CO₂ (C = 12, O = 16) is

   • A1.0
   • B0.2
   • C0.1
   • D4.4

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5. Question 25· Chemical combination· WAEC

   How many moles are there in 9.8 g of tetraoxosulphate(VI) acid, H₂SO₄? [H = 1, S = 32, O = 16]

   • A1.0
   • B0.1
   • C0.01
   • D9.8

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6. Question 26· Chemical combination· WAEC

   The mass of 0.5 mol of NaOH (Na = 23, O = 16, H = 1) is

   • A20 g
   • B40 g
   • C80 g
   • D10 g

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7. Question 27· Chemical combination· WAEC

   Calculate the percentage by mass of nitrogen in NH₃. (N = 14, H = 1)

   • A14.0%
   • B17.6%
   • C82.4%
   • D77.8%

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